The present invention relates generally to methods for use in disk drives for computer systems. More particularly, the present invention relates to methods for improving disk drive performance by determining and implementing skew settings for each drive.
Within data storage devices, e.g. disk drives, the phrase xe2x80x98seek timexe2x80x99 describes the latency realized from the initiation of a seek process until data can be transferred. If a data transfer crosses a head or cylinder boundary, i.e., data associated with the last sector of a track and the first sector of the next sequential track are included in the transfer, there is a negative impact on data throughput since the movement of data must be interrupted while a head switch or single-cylinder seek procedure is completed.
A xe2x80x98skewxe2x80x99 of a track is defined as the physical offset of logical sector zero of the target track from logical sector zero of the preceding track. The purpose of the skew is to improve disk drive performance by compensating for the rotation of the medium that occurs during the time it takes to complete a corresponding seek operation. The size of the physical offset, or the xe2x80x98skew valuexe2x80x99, is determined by the seek time associated with the required operation.
Disk drive units typically use two different track skew values, head skew and cylinder skew. Since the time required to complete a head switch operation will usually differ from that required for a single-cylinder seek, a different skew is used on the target track associated with each operation. For example, in a disk drive unit having n heads, track zero of each cylinder is always assumed to be the target track following a single-cylinder seek and is given a track skew, or cylinder skew, which is consistent with that operation. During a head switch, each of the tracks 1 through nxe2x88x921 of each cylinder is always assumed to be a target track and receives a track skew, or head skew, which is consistent with that operation.
In the past, skew values associated with a particular disk drive product were determined during the product development cycle. All disk drive units in a product line carried the same skew values. Skew values were determined by several factors, among them head mass, disk rotation speed (RPM), flexibility of the flex cable, etc. The prevailing approach was to use skew values that would avoid xe2x80x98slipped revolutionsxe2x80x99, which refers to those instances in which a data transfer is delayed a full disk revolution because of an intervening head switch or single cylinder seek operation. The ironic consequence of this approach, however, has been the use of higher skew values, resulting in longer access times, which is not conducive to high performance.
Therefore, there exists a need for a method of determining skew values for each drive and implementing the values to each drive in a manner that is conducive to high performance disk drives.
The present invention satisfies this need.
A general object of the present invention is to determine and implement skew values to improve disk drive performance.
More specifically, head skew and cylinder skew values are calculated and implemented for each drive during a production test phase of the disk drive manufacturing process.
In one aspect of the present invention, data measured during the production test phase of a disk drive manufacturing process is used to calculate and implement skew values.
These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.